<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /*(行内 id 类 标签)*/
        div p {
            color: red;
        }

        .father .son {
            color: #cccccc;
        }

        .father p {
            color: skyblue;
        }

        div #one {
            color: pink;
        }
    </style>
</head>
<body>
<div class="father">
    <p class="son" id="one">这是一个标签</p>
</div>
</body>
</html>